June 15, 2023
I think I promised an update on the tropics the other day but with all the severe weather I've been putting it off. Now that there is something in the Atlantic to watch it is a good time. The short story is that there is nothing to be concerned about along the Gulf Coast for the time being and I think it'll stay that way for a week or more. You can probably stop reading right here, but I'll give you some more details if you're curious. To start with, here is the Atlantic 7-Day Outlook:
The "x" and the yellow area is a tropical wave that will push off of Africa and may develop in a few days as it moves west (20% chance right now). I can tell you that this is fairly unusual for this time of year, we typically don't have to be concerned about this kind of development until July at the earliest. The reason we're seeing this so early is because the monsoon trough (a tropical weather feature along the intertropical convergence zone [ITCZ]) is particularly moist and making tropical waves a bit earlier than usual. Also the Atlantic is warmer than normal (over a large area, see below). These two things give us some of the ingredients we need for tropical development: a seed system (tropical wave in this case) and heat (warm water). If wind shear stays low enough as the wave moves west it may stand a chance to develop. Wind shear (the speed and direction difference between low level and high level winds) tends to keep tropical cyclones from organizing if it is strong. Looking at the models, which are prone to error at longer timeframes, there may be an area of favorable wind shear as the wave approaches the Lesser Antilles. If steering winds keep the developing system to the south and through the islands, wind shear is typically high in the eastern and central Caribbean this time of year and I wouldn't expect it to survive (doesn't mean that it won't). If it goes north of the islands towards the Bahamas and East Coast there may be favorable conditions there but I'm not sure at this point. I also don't think we'd see favorable steering conditions to bring a storm to the east coast, but it's too far out to know. My thought is that this will likely not be a threat to the US but we'll have to wait and see. Right now it'll be a week before it is near the Lesser Antilles and then a whole 'nother week at a minimum before we would be concerned.
Let's take a quick look at one more area of the tropics. Below is the 7-Day Outlook for the Eastern Pacific and you can see activity is starting to pick up there. This activity is typical for this time of year and was expected as the EPAC will (probably) have higher than normal activity due to El Nino conditions. The reason I'm pointing this out is because sometimes the zone of favorable conditions will move from the EPAC into the western Caribbean so a burst of activity there can portend activity to the east a week or two later. If this eastward movement of favorable conditions occurs and if we can get a seed system from the tail end of a cold front or from the Central American Gyre (which doesn't look to be active right now), then we might see western Caribbean development. Right now there's not much to show that any of this will happen, I just want you to be aware of a typical development pattern this time of year. As it is, any development in the EPAC should suppress western Caribbean development until any storm(s) there move off to the west and in general El Nino conditions we're having typically make development here less likely (but not impossible).
Along the same subject, if you see model graphics on social media 10+ days out showing a storm in the western Caribbean you can pretty much ignore those. The GFS model in particular this time of year has a bias where it generates spurious storms in this location. It also sometimes has trouble locating where development should occur when the EPAC is the favored area, it can inadvertently place that development too far east instead. If you have any questions about something you see, feel free to ask me.
To summarize again what I stated at the top, there are no concerns right now for the Gulf Coast even though activity in the tropics is picking up a little. The purpose of this post is to just keep you informed and to serve as a reminder on some of the things we need to look for for tropical development to occur. For the system in the Atlantic I'll send out another update once there is better info in 3-5 days.
Have a good Friday and a good weekend. I'll continue the severe weather updates as needed.
Chris
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